Calcium containing silicate oxyapatite lasers

ABSTRACT

A composition of matter which can be used as a laser crystal in a laser generator and which can be doped with sensitizer ions has the empirical chemical formula CaM4 x(SiO4)3O:Ax where A represents a lasing ion selected from Nd, Er, and Ho, x has a value from 0.001 to 1 and M represents an ion selected from La, Gd and mixtures thereof.

Bite States Patent Hopkins et al.

[4 1 Dec. 25, 1973 CALCIUM CONTAINING SILICATE OXYAPATITE LASERSInventors: Richard H. Hopkins; George W.

Roland, both of Monroeville; Kenneth B. Steinbruegge, Murrysville;William D. Partlow, Blackridge, all of Pa.

Westinghouse Electric Corporation, Pittsburgh, Pa.

Filed: 1 June 21, 1971 1 Appl. No.: 155,097

Related US. Application Data Division of Ser No. 859,673, Sept. 22,1969.

Assignee:

US. Cl. 331/945, 330/43 Int. Cl. H015 3/16 Field of Search 331/945;330/43;

[56] References Cited UNITED STATES PATENTS 3,504,300 3/1970 Mazelsky etal. 331/945 3,617,937 11/1971 Mazelsky et al. 331/945 3,686,586 8/1972Roland et al. 331/945 Primary ExaminerWilliam L. Sikes Att0rneyF. Shapoeet al.

[57] ABSTRACT A composition of matter which can be used as a lasercrystal in a laser generator and which can be doped with sensitizer ionshas the empirical chemical formula CaM (SiO O:A, where A represents alasing ion selected from Nd, Er, and Ho, x has a value from 0.001 to 1and M represents an ion selected from La, Gd and mixtures thereof.

14 Claims, 5 Drawing Figures Q SWITQH PATENTEUHECZS 1975 3. 781. 707

SHEET 10F 3 N R r A N D SENSITIZER GROU D STATE ACTIVATOR FIG. 1

PATENIEOUEC25 I925 3.781.707

I 1 sum 2 BF 3 Fluorescence Spectrum CaLa Nd 1 ISIO4I3O &

RELATIVE QUANTUM EMISSION CD I I I 1 I u WAVELENGTH, Ml CRONS FIG. 3

Excitation Spectrum CaLa g (SiO4I O:Nd 1

MUN,

l I 1 I 1 0.3 0.4 0.5 0.6 0.7 0.8 0.9

WAVELENGTH, MICRONS FIG. 5

EMISSION PER EXCTATION QUANTUM, ARBITRARY UNITS PAIENTEDDECES mm 3.781.707 sum 3 BF 3 WAVELENGTH. MICRONS FIG 4 Absorptlon Spectrum CaLa(SiO4)3:Nd

O HNI'HSVS Ol HAIIVHH 'NOISSIWSNVEU 'lVNOllOVHzl CALCIUM CONTAININGSILICATE OXYAPATITE LASERS CROSS REFERENCE TO RELATED APPLICATIONS Thisapplication is a divisional application of application U.S. Ser. No.859,673 filed on Sept. 22, 1969.

BACKGROUND OF THE INVENTION Energy transfer from one fluorescent specieto another or among fluorescent species of the same kind, is afundamental process in luminescence. Before the advent of lasers, energytransfer was widely utilized in commercial phosphors such as those usedin fluorescent lamps to improve their efficiency, and was extensivelystudied in connection with organic phosphors.

With the advent of lasers, energy transfer processes have taken onadditional importance as a means for improving the efficiency ofoptically pumped lasers. The work on fluorescent lamps was concernedmainly with the transfer of energy between transition metal ions ofdifferent types. In contrast, investigations on laser material have beenprincipally concerned with energy transfer from transition metal ionsare rare-earth ions, or energy transfer from rare-earth to rare-earthions.

The basic aim of laser energy transfer can be described as follows:given an ion which has desirable spectroscopic properties (i.e., itemits in a desirable frequency region with a suitable bandwidth etc.),but which is only a weak or inefficient absorber of the excitationenergy, one must find another ion, which has desirable absorptionproperties and which can transfer its energy efficiently and rapidly tothe emitting ion. The emitting ion is called the activator or lasing ionand the absorbing ion is called the sensitizer. Energy transfer occursfrom the sensitizer to the activator ion.

It has been demonstrated in US. Ser. No. 732,593, filed on May 28, 1969,and assigned to the assignee of this invention, that the mineralfluorapatite Ca PO )F, is an excellent host for sensitizer and/oractivator ions. Suitably doped fluorapatite exhibits high gain and lowthreshold characteristics. Large single crystals of this doped materialare prepared by Czochralski growth from stoichiometric melts attemperatures of about l,650C.

Our invention relates to a composition of matter suitable as a lasercrystal in a resonant cavity of a laser generator. Our laser materialare based on silicate oxyapatite hosts doped with neodymium, erbium orholmium. Within the limits of our measurements, these materials meltcongruently. They melt at considerably higher temperatures (about2,000-2,200C) than fluorapatite, and exhibit a higher material strength.Although the existence and synthesis of some silicate oxyapatite powdersgenerally has been disclosed, as for example by Jun Ito in 53 AmericanMineralogist 890; the growth, doping and laser application of largesingle crystals of our materials has not been previously considered.

In addition to the crystalline laser materials of this invention, otherrelated crystalline laser materials are described in Pat. ApplicationsU.S. Ser. Nos. 859,672, 859,754 and 859,753 all filed on Sept. 22, 1969and assigned to the assignee of this invention.

SUMMARY OF THE INVENTION It is a prime object of this invention toprovide a new and improved high strength composition of matter for useas a laser crystal in the resonant cavity of a laser generator.

This invention accomplishes the foregoing object by providing a silicateoxyapatite laser crystalline material having the empirical formula:

where M represents an ion selected from La, Gd and mixtures thereof. Mis considered a host constituent. This is because it is not an activatorand it plays no role as a sensitizer ion. M, a host constituent, isnecessary to the construction of the host crystal lattice and is theprime constituent for which activator and sensitizer ions aresubstituted. A represents an activator ion (lasing ion) that isresponsible for laser output. A, the activator ion, is selected from Nd,or Er or Ho. Which ion is the lasing ion, A, in the crystal can bedetermined by measuring the frequency of the laser oscillations and fromknown spectroscopic data. Generally only one lasing ion will oscillateat a time. S represents a sensitizer ion which need not be present inthe crystal. The sensitizer ion must be matched to the lasing ion. Thevalue x can vary between 0.00l-l with a preferred range between 0.00l.3and y can vary between 0 to (4-x) with a preferred range between 0 to 1.

Our laser materials have low threshold characteristics and low gainallowing improved energy storage. They also have high material strength.Our materials provide a laser crystal capable of withstanding, withoutstructural distortion, significantly higher pumping energies thanfluorapatite. Little segregation is observed in doping with neodymiumand erbium activators. This reduces serious crystal problems which existin most host due to variation in dopant segregation along the crystalcaused by temperature fluctuations during growth.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of thenature and objects of the invention, reference may be made to thefollowing drawings in which:

FIG. 1 shows energy levels of sensitizer and activator ions indicatingtransitions pertinent to energy transfer;

FIG. 2 shows a laser generator utilizing the laser crystal of thisinvention in association with a radiation source in a resonant lasercavity;

FIG. 3 shows the fluorescence spectrum of a single crystal of CaLa Nd(SiO O, unpolarized and taken along an axis perpendicular to the c axisof the crystal;

FIG. 4 shows the absorption spectrum of a single crystal of CaLa Nd (SiOO, taken along an axis perpendicular to the c axis of the crystal andthrough a thickness of 0.164 inches; and

FIG. 5 shows the excitation spectrum of the infrared fluorescence from asingle crystal of CaLa Nd ,(Si- 03 DESCRIPTION OF THE PREFERREDEMBODIMENTS The silicate oxyapatite host materials of this inventionhave the formula CaM (SiO );,O where M is an ion selected from La, Gdand mixtures thereof. These hosts contain ion sites which willaccommodate both rare earth and transition metal ions. The crystalstructure of the host materials CaLa (SiO.,) O and CaGd,,(SiO O, whereLa and Gd are host constituents, is hexagonal with unit cell formulas ofCa La (SiO O and Ca Gd (SiO O These host materials have an apatitestructurc (space group P6 /m). The Si 4 ions are in SiO tetrahedra. Twosets of 2 ions are present; one set is co-ordinated with Si 4 in the SiOtetrahedra and the other set occurs along the c axis (two ions per unitcell) with each ion co-ordinated by three cations (calcium or rareearth) in the plane of the horizontal mirror in P6 /m. Two types ofcation sites are present (Ca, or Rare Earth, and Ca or or Rare Earth Theactivator ions and/or transition metal or rare earth sensitizer ions cansubstitute for La, Gd and Ga in the host materials. This will be asubstitution of some of the five Ca and rare earth (Gd and La) cationsin the host CaM.,(Si- 03 The host materials of this invention use therare earth ions Nd 3, Er 3 or Ho 3 as their activator (lasing) ion. Theion concentration of these activators can vary in the host from about0.02 to 20 atom percent of the five cations (one Ca and four M, hostconstituent cations) in the host, CaM SiO ),,O. The preferred range ofactivator is from about 0.02 to 6 atom percent. Below the preferredrange there is generally not enough optical absorption and above thepreferred range there may be concentration quenching. Thus, x has apreferred value between 0.001 and 0.3, i.e., (0.00l=x)/ cations equals0.020 atom percent and (0.3=x)/5 cations equals 6 atom percent. Howeverwith improved flash sources for special applications it is useful tohave the value of x greater than 0.3. The sensitizer S has a preferredrange for y from 0 to l i.e., the ion concentration ofS preferablyvaries from about 0 to atom percent (1=y/5) of the five cations in thehost.

In accordance with this invention, sensitizer ions may be used tosensitize the rare earth activator ions Nd 3, Er 3 or Ho*3 in the host.Referring now to FIG. 1 which illustrates the various steps involved innonradiative energy transfer: l the sensitizer ion absorbs a photon ofexternal radiation of energy r, lifting it from the sensitizer groundstate D to an excited state A; (2) the sensitizer subsequently decays toa lower metastable state N, by the emission of a photon r or by anonradiative process; (3) once lattice relaxation about: the sensitizermetastable state has taken place, the sensitizer is either free toradiate a photon r" or to transfer its energy to an activator ion, asindicated by R; (4) if the electronic transitions in both the"sensitizer and activator are electric dipole transitions, the dipolefield of the excited sensitizer can introduce a dipole transition in anearby activator, thereby raising the activator to an excited state A,with a simultaneous return of the sensitizer to its ground state; (5)this transition transfers a quantum of energy from the sensitizer of theactivator. Once excited, the activator can decay to a lower metastablelevel N, through emissio n of hotBHsTfiEiHn eventually decay to itsground state D either directly or via an intermediate level D".Reference may be made to D. L. Dexter, J. Chem, Phys., Vol. 21, 1953,page 836 for detailed descriptions of these energy transfer processes.

The requirements in non-radiative transfer for efficient transfer ofenergy from sensitizer to activator are: (l) a reasonable overlap inenergy between the sensitizer emission band and an absorption band ofthe acti-.

vator; (2) high oscillator strengths to both sensitizer and activator;(3) a relatively high intrinsic radiative quantum efficiency for boththe sensitizer and activator. In addition to the above criteria, thereare several other criteria ofa more general nature for a usefulsensitizer. These are: l the sensitizer should absorb radiation in aspectral region where the activator has little or no absorption; (2) thesensitizer should absorb in a region where the pump lamp radiatesappreciable energy, and (3) the sensitizer should not absorb where theactivator emits, or have any adverse effects on the radiative efficiencyof the activator. For efficient energy transfer to occur it is necessarythat the rate of transfer (R in FIG. 1) be more rapid than the rate ofdecay of the sensitizer to its ground state (r" in FIG. 1).

The sensitizing ions that may be used in the composition of thisinvention would include transition metal and rare earth ions which arecapable of (a) absorbing radiation energy otherwise not absorbed by theactivator (lasing ion) and (b) transferring that absorbed energy to theactivator.

Although a variety of transition metal ions and rare earth ions aresuitable to sensitize the activator ions in the host laser crystal, bestresults are achieved when selected sensitizer ions are matched toactivator ions in the. particular host. The following table shows somesuitable combinations:

TABLE I Host Activator lon Suitable Sensitizer Ions CaLaASiOJ O Nd Mn Inthe preparation of the laser crystalline material of this invention12.0000 grams of CaCO 76.1780 grams of La O 2.0174 grams of Nd Q, and21.6022 grams of silicic acid which had been prefired at 1,300C forseveral hours to drive off water, were mixed together. All reactantswere of luminescent grade (greater than 99.9 percent purity). Theingredients were then placed in an iridium crucible and melted atapproximately 2,200C as measured by an uncorrected optical pyrometer.

Crystals were pulled from the melt at 2200C using the standardCzochralski technique, well known in the art and described in thearticle by J. Czochralski in Zeitschrift fur Physikalische Chemie, Vol.92, pages 219-221 1918). A recent description of the process is found inan article by H. Naussau and L. G. VanUitert in Journal of AppliedPhysics, Vol. 31, page 1,508

The furnace was surrounded by a quartz cylinder attached to theapparatus by means of a neoprene gasket and a brass flange. Insulationfor the iridium crucible was provided by k inch thick zirconia quadrantsstacked into a cylinder. Thermal distribution throughout the melt wascontrolled by adjusting the crucible in the field of the work coil andby changing spacing of the zirconia quadrants and the top plate. Thepower source was a Westinghouse 30 KVA motor-driven 10,000 cyclegenerator with a water cooled copper work coil. The pulling apparatuswas designed such that pull rates between 1 and 40 mm./hr and rotationspeeds of 10l70 rpm could be used. Temperature was controlled by usingthe output of a sapphire light pipe leading to a radiamatic detectorwhich fed the output into a L and N Azar recorder-controller. Thevoltage from the recorder-controller in association with an L and Ncurrent adjusting type relay supplies the input current of a Norbatrollinear power controller. The

Norbatrol output voltage supplies the necessary field excitationrequired by the 10,000 cycle generator.

The seed was held on a water cooled shaft which was threaded toaccommodate an iridium chuck. The crucible and chuck were protected fromoxidation by an argon atmosphere. Oriented seeds were used for growth.These were obtained by starting with a polycrystalline seed obtainedfrom a slow-cooled melt. Crystals were grown as large as one-half inchin diameter and 2 inches long. Cooling rates of the pulled crystalsvaried from 2 to 6 hours.

The crystalline materials grown and containing Nd, Er or Ho lasing ionsare useful as laser crystal rods in simple lasers and in morecomplicated laser applications such as Q switched lasers, both of whichare described in detail in chapters 3 and 4 and especially pages 132-160of The Laser by W. V. Smith and P. P. Sorokin, McGraw Hill, 1966, hereinincorporated by reference.

A simple schematic illustration of a typical laser generator is shown inFIG. 2 of the drawings. Between reflectors and 21 there is a resonantlaser cavity containing the laser crystal 22, a radiation source means23 such as a flash lamp which provides pump energy to the crystal, andpossibly a Q switching means shown by dotted lines. Reflector 20 ispartially reflecting to permit the escape of light beams of coherentradiation 24 whereas reflector 21 is highly reflective.

The basic principle involved in Q switching a laser is to allow a veryhigh population inversion to be built up by making the laser cavitylosses excessive, while the laser is being pumped, thereby preventingthe laser from oscillating prematurely. When a strong inversion isattained, the conditions are suddenly made favorable for oscillation byrapidly making the cavity losses very small, so that a condition oflarge amplification is suddenly realized. The Q switch could, forexample, contain a metallo-organic compound in solution such as aphthalocyanine which absorbs light from the crystal. The pumping energyinput from the flash lamp increases until amplification in the lasercrystal overcomes the loss due to absorption in the Q switch cell andthe laser begins to emit coherent light weakly. A very small amount ofthis light bleaches the solution which then becomes almost perfectlytransparent to the light. At that instant there is suddenly a giantpulse of light containing all the stored energy in the laser rod.

One of the crystals pulled at a rate of one-fourth inch per hour from amelt at about 2,200C showed laser action at a 1.06 micron wavelength.The crystal composition was CaLa Nd (SiO O. This grown boule was groundand polished. The finishing procedure on the rod end resulted inpolished ends parallel to better than 6 arc seconds and plane toone-tenth wavelength of He light. It was in the form of a 0.164 inch-X0.130 inch X 0.41 inch rectangular rod. It was tested in a 2.7 inchdiameter cylindrical reflecting cavity with flat reflectors.

pyrex reflecting cylinder 75 mm in diameter and 76 mm long having tworeflecting pyrex end plates with holes machined for the lamp and rod.Front surface evaporated aluminum coatings were used and overcoated with)t/lO quartz for protection. Resonator reflectivities were both 99.2percent. A PEK Xel-3 Xenon flashlamp was located diametrically oppositethe laser rod with a center to center spacing between The laser headused in all pulse tests was a cylindrical the lamp and rod of 0.6inches. This flashlamp was a broad band emitter with a peak emissionaround 5,800A. The laser rod was supported in a double-wall pyrexcylinder filled with a water filter solution of NaNO to prevent UV fromreaching the laser rod being tested. The flashlamp was powered by acharged 340,1.F capacitor which was discharged through a l50].l.hinductor in series with the lamp. The maximum energy into the flashlampwas held below joules to insure long life. The RLC circuit describedproduced a flashlamp pulse duration of about 800p. seconds.

Although the operating characteristics of lasers are determined by theproperties of their active lasing ions, the actual results achieved inany given system is highly dependent on imperfections in the crystal.Microscopic imperfections invisible to the eye may make laseroscillations impractical. The presence of bubbles or inclusions mayscatter the beam and increase threshold significantly.

Despite the small rod size the CaLa Nd (SiO.,) O crystal, its supposedpoor optical quality and the fact that it was oriented with the Cdirection (expected to be a low gain direction) perpendicular to theresonators, room temperature laser action was obtained at thesurprisingly low threshold at approximately 15 joules. With larger,high-quality crystals, threshold values of 4 joules should be possible.

Measurements of the laser threshold were accomplished by aligning thelaser rod in the laser head in the usual way with external reflectors. AIP25 phototube was then placed in the path of the beam with a 1.06micron interference filter between the laser and phototube to reduce thebackground signal. The phototube output was displayed on a Tektronixtype 555 dualbeam oscilloscope with one trace serving as an expandedscale. Thresholds could be accurately determined since the onset oflasing action appears as characteristic spikes as seen .with othermaterials such as ruby.

Spectroscopic data on the'fluorescence and absorption of CaLa Nd (SiO Oare shown in FIGS. 3 and 4. The fluorescence spectrum (FIG. 3), from theabove crystal shows in the near infrared including the 1.06 micronemission corresponding to the Nd laser line. In CaLa Nd ,(SiO O thisline is about ten times broader than in neodymium doped calciumfluorophosphate (50A vs. 6.5A). Hence our new silicate oxyapatite host,doped with neodymium should have enhanced energy-storage capabilitiesmaking it very promising for Q-switching laser applications. The visibleand near infrared absorption spectrum (FIG. 4) for a single crystal ofCaLa Nd ,(SiO.,) -,O indicates the considerable overlap of absorptionbands to be found in this'laser material. This'suggests a .relativelyhigh average absorption of pump radiation. The relative intensity of the1.06 micron line in its two polarizations (IF/I for this sample was 1.4and the decay time was 194 micro-seconds for the Nd emission.

The excitation spectra (FIG. 5) of the 1.06 emission line show that theenergy is transferred from the absorbing levels to the F state, theinitial laser level.

The melting point of neodymium doped CaLa (Si- 0030 is significantlyhigher than neodymium doped Ca (PO )F. we have measured the hardness ofpolycrystalline samples of these two materials and compared them in thefollowing table:

Material Knoop Hardness (200 g. load) Moh's Hardness Ca (PO )F:Nd S40 6CaLaJSiO J ONd 860 7 Thermal shock resistance of neodymium doped Ca- La(SiO O is also high, a sample suddenly subjected to an oxyhydrogen flameevidenced no spalling to the melting point. All data indicate thatCaLa.,(SiO,) O:Nd should be superior to doped calcium fluorophosphate inresisting structural distortion and failure at high pump levels.

Absorption spectra was measured on a Cary Model 14 commercialspectrometer. The excitation and fluorescence spectrometer systemconsisted of two grating monochromators for dispersing the excitinglight and fluorescence light, along with associated optics, detectors,lamps and electronics. The souce used was an Osram Type XBO-900, a highpressure xenon arc lamp which was operated from a DC supply having lessthan 1 percent ripple. Fluorescence measurements were made using aJarrel-Ash monochromator. A 600 l/mm grating blazed at 4,000A allowedexcitation spectra to be taken from 2,500 to 10,000A. The quantumdetectors used RCA 7102 Photomultipliers cooled to liquid N temperature.

We claim as our invention:

1. In a laser generator having a resonant laser cavity, a laser crystalwithin said resonant cavity and a radiation source supplying energy tothe crystal, the improvement comprising a silicate oxyapatite lasercrystal having the formula, CaM SiO O wherein M is an ion selected fromthe group consisting of La, Gd and mixtures thereof, said crystalcontaining an activator ion selected from the group consisting of Nd,Br, and H0 in the ion concentration range of 0.02 to 20 atom percent ofthe calcium and M cations in the crystal.

2. The laser generator of claim 1 wherein the crystal contains theactivator ion Nd in the ion concentration range of 0.02 to 6 atompercent.

3. The laser generator of claim 1 also containing a Q switching means.

4. In a laser generator having a resonant laser cavity, a laser crystalwithin said resonant cavity and a radiation source supplying energy tothe crystal, the improvement comprising a silicate oxyapatite lasercrystal having the formula CaM (SiO -,O:A,S, where M is an ion selectedfrom the group consisting of La and Gd, A is the ion Nd, S is thesensitizer ion Mn, wherein A is present in the ion concentration rangeof 0.02 to 20 atom percent of the calcium and M cations in the formulaand S is present in the ion concentration range of 0 to 20 atom percentof the calcium and M cations in the formula.

5. The laser generator of claim 4 wherein the ion concentration of S isO in the laser crystal.

6. The laser generator of claim 4 also containing a 0 switching means.

7. In a laser generator having a resonant laser cavity, a laser crystalwithin said resonant cavity and a radiation source supplying energy tothe crystal, the improvement comprising a silicate oxyapatite lasercrystal having the empirical formula CaM ,,(SiO,,) O:A Sy, wherein M isan ion selected from the group consisting of La and Gd, A is the ion Er,S is the sensitizer ion Yb, x has a value between 0.001 and l and y hasa value between 0 and (4-x).

8. The laser generator of claim 7 also containing a 0 switching means.

9. The laser generator of claim 7, wherein y has a value between 0 and land x has a value between 0.001 and 0.30 in the laser crystal.

10. The laser generator of claim 9, wherein y=0 in the laser crystal.

11. in a laser generator having a resonant laser cavity, a laser crystalwithin said resonant cavity and a radiation source supplying energy tothe crystal, the improvement comprising a silicate oxyapatite lasercrystal having the empirical formula CaM ,,(SiO.,) O:A S wherein M is anion selected from the group consisting of La and Gd, A is the ion Ho, Sis a sensitizer ion selected from the group consisting of Cr, Tm, Er,and Yb, x has a value between 0.001 and l and y has a value between 0and (4-x).

12. The laser generator of claim 11 also containing a Q switching means.

13. The laser generator of claim 11, wherein y has a value between 0 andl and x has a value between 0.00l and 0.30 in the laser crystal.

14. The laser generator of claim 13, wherein y=0 in the laser crystal.

2. The laser generator of claim 1 wherein the crystal contains theactivator ion Nd in the ion concentration range of 0.02 to 6 atompercent.
 3. The laser generator of claim 1 also containing a Q switchingmeans.
 4. In a laser generator having a resonant laser cavity, a lasercrystal within said resonant cavity and a radiation source supplyingenergy to the crystal, the improvement comprising a silicate oxyapatitelaser crystal having the formula CaM4(SiO4)3O:A,S, where M is an ionselected from the group consisting of La and Gd, A is the ion Nd, S isthe sensitizer ion Mn, wherein A is present in the ion concentrationrange of 0.02 to 20 atom percent of the calcium and M cations in theformula and S is present in the ion concentration range of 0 to 20 atompercent of the calcium and M cations in the formula.
 5. The lasergenerator of claim 4 wherein the ion concentration of S is O in thelaser crystal.
 6. The laser generator of claim 4 also containing a Qswitching means.
 7. In a laser generator having a resonant laser cavity,a laser crystal within said resonant cavity and a radiation sourcesupplying energy to the crystal, the improvement comprising a silicateoxyapatite laser crystal having the empirical formulaCaM4-x-y(SiO4)3O:Ax, Sy, wherein M is an ion selected from the groupconsisting of La and Gd, A is the ion Er, S is the sensitizer ion Yb, xhas a value between 0.001 and 1 and y has a value between 0 and (4-x).8. The laser generator of claim 7 also containing a Q switching means.9. The laser generator of claim 7, wherein y has a value between 0 and 1and x has a value between 0.001 and 0.30 in the laser crystal.
 10. Thelaser generator of claim 9, wherein y 0 in the laser crystal.
 11. In alaser generator having a resonant laser cavity, a laser crystal withinsaid resonant cavity and a radiation source supplying energy to thecrystal, the improvement comprising a silicate oxyapatite laser crystalhaving the empirical formula CaM4-x-y(SiO4)3O:Ax, Sy, wherein M is anion selected from the group consisting of La and Gd, A is the ion Ho, Sis a sensitizer ion selected from the group consisting of Cr, Tm, Er,and Yb, x has a value between 0.001 and 1 and y has a value between 0and (4-x).
 12. The laser generator of claim 11 also containing a Qswitching means.
 13. The laser generator of claim 11, wherein y has avalue between 0 and 1 and x has a value between 0.001 and 0.30 in thelaser crystal.
 14. The laser generator of claim 13, wherein y 0 in thelaser crystal.